We take turns driving long distance job to job. When my co-worker drives he texts and drives erratically. I'm a nervous wreck and would prefer to do all the driving. My co-worker is a supervisor with more tenure. I am a fairly new employee.

Are you required to go with your supervisor? Can you just drive yourself? If you don't have an option, you should mention to your supervisor that you are uncomfortable with his/her texting while driving. Your life is at stake.